External Charger for an Implantable Medical Device System Having a Coil for Communication and Charging

ABSTRACT

Disclosed in an improved medical implantable device system including an improved external charger that is able to communicate with an external controller and IPG using the communication protocol (e.g., FSK) used to implement communications between the external controller and the implant. The external controller as modified uses its charging coil to charge the implant, and also to communicate with the other devices in the system. As such, the external charger is provided with transceiver circuitry operating in accordance with the protocol, and also includes tuning circuitry to tune the coil as necessary for communications or charging. Communication or charging access to the charging coil in the external charger is time multiplexed. The disclosed system allows charging information to be provided to the user interface of the external controller so that it can be reviewed by the user, who may take corrective action if necessary. Also disclosed are schemes for synchronizing and arbitrating communications between the devices in the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.13/647,200, filed Oct. 8, 2012, which is a non-provisional of U.S.Provisional Patent Application Ser. No. 61/558,601, filed Nov. 11, 2011.Priority is claimed to both of these applications, and both areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an improved implantable medical devicesystem having a communication link between an external controller and anexternal charger.

BACKGROUND

Implantable stimulation devices are devices that generate and deliverelectrical stimuli to nerves and tissues for the therapy of variousbiological disorders, such as pacemakers to treat cardiac arrhythmia,defibrillators to treat cardiac fibrillation, cochlear stimulators totreat deafness, retinal stimulators to treat blindness, musclestimulators to produce coordinated limb movement, spinal cordstimulators to treat chronic pain, cortical and deep brain stimulatorsto treat motor and psychological disorders, and other neural stimulatorsto treat urinary incontinence, sleep apnea, shoulder sublaxation, etc.The description that follows will generally focus on the use of theinvention within a Spinal Cord Stimulation (SCS) system, such as thatdisclosed in U.S. Pat. No. 6,516,227. However, the present invention mayfind applicability in any implantable medical device system. Forexample, the disclosed invention can also be used with a Bion™implantable stimulator, such as is shown in U.S. Patent Publication2007/0097719, or with other implantable medical devices.

As shown in FIGS. 1A and 1B, a SCS system typically includes anImplantable Pulse Generator (IPG) 100, which includes a biocompatibledevice case 30 formed of titanium for example. The case 30 typicallyholds the circuitry and battery 26 necessary for the IPG to function,although IPGs can also be powered via external RF energy and without abattery. The IPG 100 is coupled to electrodes 106 via one or moreelectrode leads (two such leads 102 and 104 are shown), such that theelectrodes 106 form an electrode array 110. The electrodes 106 arecarried on a flexible body 108, which also houses the individual signalwires 112 and 114 coupled to each electrode. In the illustratedembodiment, there are eight electrodes on lead 102, labeled E₁-E₈, andeight electrodes on lead 104, labeled E₉-E₁₆, although the number ofleads and electrodes is application specific and therefore can vary. Theleads 102 and 104 couple to the IPG 100 using lead connectors 38 a and38 b, which are fixed in a header material 36, which can comprise anepoxy for example. In a SCS application, electrode leads 102 and 104 aretypically implanted on the right and left side of the dura within thepatient's spinal cord. These leads 102 and 104 are then tunneled throughthe patient's flesh to a distant location, such as the buttocks, whereinthe IPG 100 is implanted.

As shown in cross section in FIG. 3, the IPG 100 typically includes anelectronic substrate assembly 14 including a printed circuit board (PCB)16, along with various electronic components 20, such as amicrocontroller, integrated circuits, and capacitors mounted to the PCB16. Two coils are generally present in the IPG 100: a telemetry coil 13used to transmit/receive data to/from an external controller 12; and acharging coil 18 for charging or recharging the IPG's battery 26 usingan external charger 50. The telemetry coil 13 can be mounted within theheader 36 of the IPG 100 as shown.

FIG. 2 shows plan views of the external controller 12 and the externalcharger 50, and FIG. 3 shows these external devices in cross section andin relation to the IPG 100 with which they communicate. The externalcontroller 12, such as a hand-held programmer or a clinician'sprogrammer, is used to send data to and receive data from the IPG 100.For example, the external controller 12 can send programming data suchas therapy settings to the IPG 100 to dictate the therapy the IPG 100will provide to the patient. Also, the external controller 12 can act asa receiver of data from the IPG 100, such as various data reporting onthe IPG's status. As shown in FIG. 3, the external controller 12, likethe IPG 100, also contains a PCB 70 on which electronic components 72are placed to control operation of the external controller 12. Theexternal controller 12 is powered by a battery 76, but could also bepowered by plugging it into a wall outlet for example. A telemetry coil73 is also present in the external controller 12, which coil will bediscussed further below.

The external controller 12 typically comprises a user interface 74similar to that used for a portable computer, cell phone, or other handheld electronic device. The user interface 74 typically comprisestouchable buttons 80 and a display 82, which allows the patient orclinician to send therapy programs to the IPG 100, and to review anyrelevant status information reported from the IPG 100.

Wireless data transfer between the IPG 100 and the external controller12 preferably takes place via inductive coupling. This typically occursusing a well-known Frequency Shift Keying (FSK) protocol, in which logic‘0’ bits are modulated at a first frequency (e.g., 121 kHz), and logic‘1’ bits are modulated at a second frequency (e.g., 129 kHz). Toimplement such communications, both the IPG 100 and the externalcontroller 12 have coils 13 and 73 respectively. Either coil can act asthe transmitter or the receiver, thus allowing for two-way communicationbetween the two devices. Referring to FIG. 4, when data is to be sentfrom the external controller 12 to the IPG 100 (FSK link 170), coil 73is energized with alternating current (AC), which generates a magneticfield, which in turn induces a voltage in the IPG's telemetry coil 13.The generated magnetic field is FSK modulated (120) in accordance withthe data to be transferred. The induced voltage in coil 13 can then beFSK demodulated (125) at the IPG 100 back into the telemetered datasignals. Data telemetry in the opposite direction (FSK link 172) fromIPG 100 to external controller 12 occurs similarly. This means ofcommunicating by inductive coupling is transcutaneous, meaning it canoccur through the patient's tissue 25.

The external charger 50 is used to charge (or recharge) the IPG'sbattery 26. Specifically, and similarly to the external controller 12,the external charger 50 contains a coil 88 which is energized viacharging circuit 122 with a non-modulated AC current to create amagnetic charging field (174). This magnetic field induces a current inthe charging coil 18 within the IPG 100, which current is rectified(132) to DC levels, and used to recharge the battery 26, perhaps via acharging and battery protection circuit 134 as shown. The frequency ofthe magnetic charging field (e.g., 80 kHz) may differ from that used forFSK telemetry (nominally 125 kHz). Again, inductive coupling of power inthis manner occurs transcutaneously.

The IPG 100 can also communicate data back (176) to the external charger50 using Load Shift Keying (LSK) modulation circuitry 126. LSKmodulation circuitry 126 receives data to be transmitted back to theexternal charger 50 from the IPG's microcontroller 150, and then usesthat data to modulate the impedance of the charging coil 18. In theillustration shown, impedance is modulated via control of a loadtransistor 130, with the transistor's on-resistance providing thenecessary modulation. This change in impedance is reflected back to coil88 (LSK link 176) in the external charger 50, which interprets thereflection at LSK demodulation circuitry 123 to recover the transmitteddata. This means of transmitting data from the IPG 100 to the externalcharger 50 is useful to communicate data relevant to charging of thebattery 26 in the IPG 100, such as the battery level, whether chargingis complete and the external charger can cease, and other pertinentcharging variables. However, because LSK works on a principle ofreflection, such data can only be communicated from the IPG 100 to theexternal charger 50 during periods in which the external charger 50 isactive and is producing a magnetic charging field (174).

As shown in FIG. 3, the external charger 50 generally comprises at leastone printed circuit board 90, electronic components 92 which controloperation of the external charger 50, and a battery 96 for providingoperational power for the charger 50 and for the production of themagnetic charging field. Like the external controller 12, the externalcharger 50 has a user interface 94 to allow the patient or clinician tooperate the charger 50. The user interface 94 typically comprises anon/off switch 95 which activates the production of the magnetic chargingfield; an LED 97 to indicate the status of the on/off switch 95; and aspeaker 98 for emitting a “beep” at various times. For example, thespeaker 98 can beep if the charger 50 detects that its coil 88 is not ingood alignment with the charging coil 18 in the IPG 100. Alignmentinformation can be determined and indicated to the external charger 252by alignment circuitry 103, which is well-known in the art. In a SCSapplication in which the IPG 100 is implanted in the patient's buttocks,the external charger 50 is generally positioned behind the patient andheld against the patient's skin or clothes and in good alignment withthe IPG 100 by a belt or an adhesive patch, which allows the patientsome mobility while charging.

As one might appreciate from the foregoing description, the userinterface 94 of the external charger 50 is generally simpler than theuser interface 74 of the external controller 12. Such user interfacesimplicity is understandable for at least two reasons. First is therelative simplicity of the charging function the external charger 50provides. Second, a complicated user interface, especially one havingvisual aspects, may not be warranted because the external charger 50 maynot be visible to the patient when it is used. For example, in a SCSapplication, the external charger 50 would generally be behind thepatient to align properly with the IPG 100 implanted in the buttocks asjust discussed. The external charger 50 would not be visible in thisposition, and thus providing the user interface 94 of the externalcharger 50 with a display or other visual indicator would be ofquestionable benefit. Additionally, the external charger 50 may becovered by clothing, again reducing the utility of any visual aspect tothe user interface.

Although the simplicity of the user interface 94 of the external charger50 is understandable, the inventor still finds such simplicityregrettable. Even if operation of the external charger 50 is relativelysimple, the fact remains that several pieces of information relevant tothe charging process might be of interest to the patient, which charginginformation is impractical or impossible to present by audible meanssuch as through speaker 98.

For example, it may be desired for the user to have some informationconcerning the alignment between the external charger 50 and the IPG100; the status of the IPG's battery 26, i.e., to what level it ischarged; how much longer charging might take; the status of the externalcharger's battery 96; or the temperature of either the external charger50 or the IPG 100. Temperature information can be particularly importantto know for safety reasons, and can be provided by a thermocouple 101 inthe external charger, and a thermocouple in the IPG (not shown).Inductive charging can heat both the external charger 50 and the IPG100, and if temperatures are exceeding high, injury or tissue damage canresult. Regardless, despite the importance of such charging information,the user interface 94 does not present such information to the user.

One approach in overcoming these shortcomings is disclosed in U.S.Patent Publication 2010/0305663 (“the '663 Publication”), filed Jun. 2,2009, and incorporated herein by reference in its entirety. As shown inFIG. 5, the '663 Publication provides an RF communication link 210between the external charger 50 and the external controller 12 so thatthey can communicate with each other. RF communication link 210 isenabled by an RF transceiver 202 and an RF antenna 202 a in the externalcontroller 12, and a corresponding RF transceiver 200 and antenna 200 ain the external charger 50. Link 210 preferably comprises a Bluetooth™compliant link, or other suitable RF communications protocol such asZigbee™ WiFi, etc.

The external charger 50 and the IPG 100 can generate a variety ofcharging information such as those parameters just mentioned that can betransmitted to the external controller 12, where it can be reviewed andcontrolled by the external controller's 12 user interface 74, which asnoted is more sophisticated and easier to view. For example, using RFcommunication link 210, the user can review the relevant charginginformation from the external charger 50. Relevant charging informationfrom the IPG 100 such as battery 26 status and temperature can betransmitted via LSK link 176 to the external charger 50, and then sentto the external controller 12 via the RF communication link 210, orcould be sent directly to the external controller 12 via FSK link 172.FIG. 6 shows the user interface 74 of the external controller 12displaying such charging information 232 on its display 82. Someprocessing of the charging information may occur first in the externalcontroller 12 before it is presented in this manner.

While the system of the '663 Publication provides desirable versatility,the inventors recognize a few drawbacks. For example, the system addsadditional hardware components to the external charger 50 and theexternal controller 12 such as transceivers 200 and 202, antennas 200 aand 202 a, etc. This additional hardware adds cost, in terms of powerand expense, and complexity to the system.

Given these shortcomings, the art of implantable medical devices wouldbenefit from an improved means for providing relevant charginginformation to a patient, and this disclosure presents solutions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show an implantable pulse generator (IPG), and themanner in which an electrode array is coupled to the IPG in accordancewith the prior art.

FIG. 2 shows plan views of an external controller and an externalcharger which communicate with an IPG in accordance with the prior art.

FIG. 3 shows cross sectional views of the external controller, theexternal charger and the IPG of FIGS. 1 and 2, and shows thecommunicative relations between these devices.

FIGS. 4 and 5 show communication circuitry present in the externalcontroller, the external charger, and the IPG in accordance with theprior art.

FIG. 6 shows the user interface of the external controller, and how thatinterface can display charging information in accordance with the priorart.

FIG. 7 shows an improved system in which the external controller and theexternal charger establish a communication link by using the chargingcoil of the external charger in accordance with an embodiment of thepresent invention.

FIG. 8 shows additional details of the external charger of FIG. 7 inaccordance with an embodiment of the present invention.

FIGS. 9A-9D show time-domain-multiplexed communications between theexternal charger, the external controller and the IPG of the system ofFIG. 7 in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The description that follows relates to use of the invention within aspinal cord stimulation (SCS) system. However, it is to be understoodthat the invention is not so limited. Rather, the invention may be usedwith any type of implantable medical device system. For example, thepresent invention may be used in a system employing an implantablesensor, an implantable pump, a pacemaker, a defibrillator, a cochlearstimulator, a retinal stimulator, a stimulator configured to producecoordinated limb movement, a cortical and deep brain stimulator, or inany other neural stimulator system configured to treat any of a varietyof conditions.

Disclosed is an improved medical implantable device system including animproved external charger that is able to communicate with an externalcontroller and IPG using the communication protocol (e.g., FSK) used toimplement communications between the external controller and theimplant. The external charger as modified uses its charging coil tocharge the implant as is normal, and also to communicate with the otherdevices in the system. As such, the external charger is provided withtransceiver circuitry operating in accordance with the protocol, andalso includes tuning circuitry to tune the coil as necessary forcommunications or charging. Communication or charging access to thecharging coil in the external charger is time multiplexed. The disclosedsystem allows charging information to be provided to the user interfaceof the external controller so that it can be reviewed by the user, whomay take corrective action if necessary. Also disclosed are schemes forsynchronizing and arbitrating communications between the devices in thesystem.

FIG. 7 discloses an embodiment of the improved system 201, which systemcomprises an IPG 100, an improved external charger 252, and an improvedexternal controller 254. Unlike previously-known approaches which useseparate antennas and transceiver circuits for communicating databetween the external charger and the external controller, the improvedsystem 201 uses the charging coil 88 in the external charger 252 forcommunicating data to the external controller 254 via link 251. Link 251preferably operates in accordance with the same protocol that is used bycommunication links 170 and 172 between the external controller 254 andthe IPG 100, e.g., FSK. Additionally, because the coil 88 in theexternal charger 252 is FSK compliant, it may additionally communicatewith the IPG 100 via an FSK link 266. Rendering the external charger 50to be FSK compliant in this fashion requires only minimal changes to theexternal charger 50, and requires no hardware changes to either theexternal controller 254 or the IPG 100. Moreover, and as will be seenbelow, improving the communicative flexibility between these devices insystem 201 allows charging information to be easily sent to the externalcontroller 254, where such data can be processed and presented to theuser interface 74 of the external controller.

Legacy communications in system 201 remain unaffected. Thus, theexternal controller 254 and IPG 100 can still communicate via FSK viadata links 170 and 172. And the external charger 252 can still provide amagnetic charging field (174) to the IPG 100. Moreover, the IPG 100 canstill communicate data back to the external charger 252 via LSK, and assuch the external charger 252 can still include LSK demodulationcircuitry 123 (FIG. 4) if desired, although this is not shown in FIG. 7.As will be seen, there is less, or no, need in system 201 for LSKtelemetry given the preferred use of FSK link 266 to communicate betweenthe external charger 252 and the IPG 100.

The external charger 252 is modified in FIG. 7 to include a transceivercircuit 255, which includes a FSK modulator circuit 265, and a FSKdemodulator circuit 256. The FSK modulator and demodulator circuits 265and 256 can be similar to the FSK modulator and demodulator circuits 120and 121 of the external controller 254. The external charger 252 alsoincludes a tuning circuit 253 for tuning the coil 88 appropriately forboth charging and FSK telemetry.

FIG. 8 illustrates the external charger 252 in further detail. Tuningcircuit 253 includes charging capacitor Cch 259, a data capacitor Cdt257, and a switch 258 controlled by a control signal K1 issued form theexternal charger's microcontroller 144. The series combination of theswitch 258 and Cch 259 is connected in parallel with Cdt 257. Switch 258can take one of two positions: open/off when the external charger 252 isbeing used to telemeter or receive data, and closed/on when it is beingused to charge the IPG 100. When switch 258 is open during telemetry,Cch 259 is disconnected from the coil 88 resulting in a series resonanttank circuit formed by the coil 88 and Cdt 257 which resonates at afrequency suitable for FSK telemetry, e.g., 125 kHz. When switch 258 isclosed, Cch 259 appears in parallel with Cdt 257, increasing theeffective capacitance in series with coil 88 and lowering the frequencyto that suitable for charging, e.g., 80 kHz.

Microcontroller 144 in the external charger 252 also controls chargecircuit 122 and transceiver circuitry 255 at appropriate times,depending on whether charging or telemetry is taking place. For example,microcontroller 144 can turn off the charging circuit 122 or put it inhigh impedance state during data telemetry or during periods when theexternal charger 252 is listening for an incoming data transmission sothat the charging circuit 122 does not load or affect the transceivercircuit 255. Likewise, the microcontroller 144 can turn off thetransceiver circuit 255 or put it in high impedance state so that itdoes not load or affect the charging circuit 122 during charging.Although not shown, control signal K1 can also be received by chargingcircuitry 122 and transceiver circuitry 255 to inform those modules whatmode (telemetry or charging) the external charger is operating in, andto respond appropriately.

While the external charger 252 is capable of carrying out datacommunication with the external controller 254, its primary purpose isto charge the IPG 100. Time spent by the external charger 252 incommunicating with the external controller 254 or the IPG 100 is timespent not charging the IPG 100, which can result in longer chargingtimes. Therefore, the external charger 252 is designed to maximize theamount of time spent charging the IPG 100, and only intermittentlydiscontinues charging to communicate with the external controller 254 orthe IPG 100 when necessary, as will be seen.

The external charger 252 can alternate between communicating telemetrydata with the external controller 254 and charging the IPG 100 using twomodes of operation: a fast data transmit mode, and a slow data transmitmode. The fast data transmit mode is particularly useful when theexternal charger 252 needs to provide near real-time charginginformation to the external controller 254. One example of this would bewhen the external charger 252 needs to provide alignment data to informthe user about the position of the external charger 252 relative to theIPG 100. It is desired to display such information relatively quickly onthe display 82 of the external controller 254 so that the user can takequick corrective action in repositioning the external charger 252 ifnecessary. By contrast, other charging information, such as batterylevel, or alignment information once initial good alignment has beenachieved, need not be presented at the external controller 254 asquickly, and instead this data can be uploaded to the externalcontroller 254 in the slow data transmit mode with less frequency andwith some latency, which is less disruptive of charging.

FIGS. 9A-9D illustrate timing diagrams to further describe the operationof system 201, and discusses in detail the data transmit modes justmentioned as well as other means of effecting communications between theexternal charger 252, the external controller 254, and the IPG 100. Thetimings illustrated in the Figures can be implemented and controlled byprogramming of the microcontrollers 144, 142, and 150 respectively inthe external charger 252, the external controller 254, and the IPG 100.It should be noted that the various communication shown in FIGS. 9A-9Doccur by FSK, either via FSK link 251 between the external charger 252and the external controller 254, or link 266 between the externalcharger 252 and the IPG 100. Time-multiplexed access to the coil 88 inthe external charger 252, and appropriate enablement of the chargingcircuitry 122, the FSK transceiver circuitry 255, and tuning circuitry253, would occur as previously described. Timings for the variousperiods shown in FIGS. 9A-9D are shown at the bottom of each figure, butthese are merely non-limiting examples. Timing may not be drawn toscale.

In the depicted example of the system 201, the external controller 254takes precedence over the external charger 252, and can control theexternal charger 252 such as by turning the charger on or off, orrequesting information from the charger as necessary. It is beneficialto arbitrate communications in this way because the charging fieldcreated by the external charger 252 (174, FIG. 7) can interfere with FSKcommunications. As such, when the external controller 254 wishes tocommunicate with either the external charger 252 or the IPG 100, thecontroller notifies the charger of that fact so that the charger cantemporarily suspend production of the charging field.

As a result, the external charger 252 must periodically listen forcommunications from the external controller 254, as is shown starting inFIG. 9A. In FIG. 9A, the external charger 252 is operating as it does ina normal legacy system to provide a charging field. Thus, the patienthas turned on the external charger 252 to produce a charging field tocharge the battery 26 in the IPG 100. Such charging occurs duringcharging periods CF 401, which may last for a duration of 190 ms forexample. Interspersed between these periods CF are listening windows LW407, during which the external charger 252 listens for telemetry fromexternal controller 254, which is not presently operating in FIG. 9A.The duration of the listening windows LW 407 may be 10 ms long in oneexample, which is small in comparison to the duration of the chargingfields. Therefore, while the listening windows LW 407 increase theoverall time needed to charge the battery 26 in the IPG 100, suchinterruptions are small, and generally transparent to the patient.

Eventually, the patient may turn off the external charger 252, or thecharger may suspend charging per its normal operation when notified (byLSK telemetry for example) the battery 26 is fully charged, as shown bythe absence of charging periods CF at the right side of FIG. 9A. At thispoint, the external charger 252 is in a power-down (low power, or sleep)state, but still periodically listens for telemetry from the externalcontroller 254. Keeping the external charger 252 in a power-down stateis reasonable given the relative large battery 96 (FIG. 3) within thecharger. Once the external charger 252 is no longer producing a chargingfield, the spacing 414 between the listening windows LW 407 can beincreased significantly to save power. Moreover, all the while, the IPG100 has also been listening for telemetry requests during listeningwindows 415, as it does in legacy systems.

FIG. 9B illustrates use of the external controller 254 to receivecharging information of the types previously discussed. Providingcharging information to the external controller 254 can commence at anyreasonable time during operation of the external controller 254, such aswhen the patient accesses an appropriate menu to review suchinformation, as shown in FIG. 6 for example. Regardless of how or whenthis occurs, the external controller 254 transmits a first command TC1to the external charger 252 along link 251 (FIG. 7), which in effectstarts a “handshaking” procedure between the controller and charger.Prior to this, the external charger 252 may have been in the power-downstate, or may have already been providing a charging field, as shown bythe dotted line around period 401 at the left of FIG. 9B. If powereddown, the external controller 254 will eventually turn on the externalcharger 252 so that it can produce a charging field and thus provide thecharging information of interest, as will be seen shortly.

This first command TC1 requests an acknowledgment AK 306 from thecharger 252, and alerts the external charger 252 to begin listening forfurther commands. The duration of TC1 is typically long enough tocoincide with one of the external charger's listening windows LW, suchas LW 407 a in the illustrated example, and is repeated to ensure thatit can be fully received during a window LW 407. The TC1 command caninclude in one example 19 bytes of alerting code recognizable by theexternal charger 252, 3 bytes of containing the device ID of the charger252, 1 byte of command (in this case, requesting an acknowledgment), andtwo bytes of error checking code (e.g., Cyclic Redundancy Check (CRC)data). The device ID ensures that the proper device in thesystem—external charger 252—will respond as opposed to the IPG 100 orsome other external charger or other external device.

The external charger 252 acknowledges receiving command TC1 with anacknowledgment AK 306, which is received at the external controller 254during duration RX 303. AK 306 can also by default include statusinformation, including the charging information, or such information maycome later after handshaking. The external controller 254 then transmitsanother command, TC2, which instructs the external charger 252 toproduce a charging field for charging the IPG 100, in case it is notproviding one already. TC2 can be formatted similar to TC1 as justdescribed. The external charger 252 receives command TC2 duringlistening window LW 407 b, and replies with transmission RP 307. LW 407b can be longer than other listening windows as the external charger 252is on notice that it will be receiving a possibly longer command TC2. RP307 notifies the external controller 254 of the receipt of the command,as received during duration RX 304, and may again also include somestatus information.

As noted earlier, the external charger 252 can operate in fast datatransmit mode or in slow data transmit mode, which mode of operation, inone example, can be determined based on the level of alignment betweenthe external charger 252 and the IPG 100. In the example provided inFIG. 9B, the external charger 252 begins operation in the fast datatransfer mode as a default once it has handshaken with the externalcontroller 254 in the manner just described. This is preferred even ifthe external charger 252 is already well aligned with the IPG 100, i.e.,if alignment circuitry 103 already indicates sufficient alignment, whichit very well may be if it were already providing a charging field to theIPG 100 (FIG. 9A). If alignment is already sufficient, or if alignmentis achieved quickly, then the system will not remain the fast datatransfer mode for long, as will be described below.

In fast data transmit mode, the external charger 252 alternates betweenperiods CF′ 402 and SX 403, each with relatively equal duration. Duringperiods CF′ 402, the external charger 252 charges the IPG 100 byproducing a magnetic charging field at coil 88, and in state SX 403 ittransmits charging information, such as alignment information providedfrom alignment circuitry 103 and possibly other charging parametersalready mentioned, to the external controller 254. The externalcontroller 254 receives this information during periodic receivesperiods RX′ 305, which correspond with the SX transfers from theexternal charger 252. The external controller 254 can infer from thereceived alignment information whether the external charger 252 isoperating in a fast data transmit mode, and accordingly can schedule thereceive period RX′ 305 at appropriate times so that data transfer duringstates SX is synchronized. Alternatively, the SX transmission canspecifically include an indication of the external charger 252's datatransfer mode.

Once the charging information is received at the external controller254, it can be processed if necessary and forwarded to the display 82device for user review. By alternating relatively rapidly between CF andSX, the external charger 252 provides near-real-time alignmentinformation to the user, which allows the user to take quick responsiveaction to try and better position the external charger 252 relative tothe IPG 100. Although during the fast data transmit mode charging of theIPG battery 26 would be twice as slow, this mode should not last forlong, and the battery 26 is still being charged to some degree.

Eventually, the user will be able to align the external controller 254with the IPG 100, which is indicated in FIG. 9B at time 312. At thispoint, the fast data transmit mode between the external charger 252 andexternal controller 254 could cease, and a slow data transmit modeentered. However, in the illustrated example, these devices continue tooperate in fast data transmit mode during period 405 to account for anyadditional movement by the user to fine tune the alignment, which can beon the order of seconds. During period 405, alignment circuitry 103 cancontinue to be checked by the external charger 252 to ensure that goodalignment continues to be established, and that the fast data transfermode can eventually be left. After period 405, the external charger 252enters the slow data transmit mode, and the external controller 254stops listening for SX, and thus receive periods RX′ 305 are no longerpresent. Again, the external controller 254 will know based on thereceived alignment information when the external charger 252 has leftthe fast data transfer mode and when period 405 has ceased.

After period 405, the external charger 252 enters the slow data transmitmode as just noted, which is illustrated in FIG. 9C. In slow datatransmit mode, the external charger 252 continues charging the IPG 100during periods CF 401, but continues periodically listening for anytelemetry from the external controller 254 during listening windows LW407. The external charger 252 also requests relevant charginginformation from the IPG 100, such as its battery level and temperature.Eventually, the external charger 252 will package the IPG's charginginformation with the external charger's charging information to theexternal controller 254.

Procuring IPG charging information occurs by external charger 252transmitting a command TI1 to the IPG 100 along link 266 (FIG. 7). Theduration of TI1 is typically long enough to coincide with one of theIPG's listening windows LW, such as LW 415 a in the illustrated example,and is repeated to ensure that it can be fully received during alistening window LW 415. The TI1 command can include in one example 19bytes of alerting code, 3 bytes containing device ID of the IPG 100, 1byte of command requesting status information, and 2 bytes of errorcorrecting code (e.g., CRC)—similar to the commands sent from theexternal controller 254 to the external charger 252 (FIG. 9B).

Upon receiving the TI1 command, the IPG 100 transmits a reply RP 439,which includes the required IPG charging information. Synchronization ofthis reply 439 and receipt 426 at the external charger 252 can be ensureby having the IPG 100 extended listening window until it no longerreceives any data, i.e., when the end of command TI1 is sensed. Theexternal charger 252 can store the charging information received fromthe IPG 100 in memory. The external charger 252 can repeatedly query theIPG 100 to update the stored charging information. It is preferred forsimplicity that data transfer between the external charger 252 and theIPG 100 occur in this manner illustrated, instead of implementing ahandshaking/acknowledgment/reply type scheme as used between theexternal controller 254 and the external charger, although thismore-complicated scheme could also be used. After receiving the charginginformation from the IPG 100, the external charger 252 can return tocharging the IPG 100 by continuing to intersperse charging filed periodsCF 401 and listening windows 407.

Eventually, the external controller 254 will request charginginformation from the external charger 252, although because the system201 is now operating a slow data transmit mode, this may occur moresporadically, e.g., even ten seconds or so. To transfer the charginginformation, the external controller 254 sends command TC3 and TC4 tothe external charger 252 coincident with listening windows LW 407 c and407 d. This handshake and data exchange is similar to that describedearlier with respect to commands TC1 and TC2, and so such details arenot repeated here. In any event, the external charger's reply 432provides the charging information—both the external charging informationand the IPG charging information—to the external controller during RX421. Again, this transmission occurs more slowly, but sufficientlyquickly to update the display 82 in the external controller with therelevant charging information. After this, the external charger 252 cancontinue charging (401) and listening (407) as before.

If at any time during the slow data transmit mode the external charger252 becomes misaligned with the IPG 100, such would be reported by thealignment circuitry 103 in the external charger 252, and wouldeventually be reported to the external controller 254. As such, theexternal controller 254 can once again instigate the fast transmissionmode via commands TC1 and TC2 as described earlier with respect to FIG.9B.

FIG. 9D shows control of the external charger 252 when the externalcontroller 254 needs to communicate data with the IPG 100, as is itslegacy function. This could occur for example if the patient is tryingto change the therapy being provided by the IPG 100. In thiscircumstance, the external controller 254 may not necessarily know ifthe patient is currently operating his external charger 252 to chargethe IPG's battery. As mentioned earlier, the charging field produced bythe external charger 252 may interfere with FSK communications betweenthe external controller 254 and the IPG 100. As such, having thecharging field activated during communications between the externalcontroller 254 and the IPG 100 is unadvisable. One way of getting aroundthis problem would be to alert the user to manually shut off theexternal charger 252 before beginning communications between theexternal controller 254 and the IPG 100. But this puts additionaloperational burden on the user.

FIG. 9D illustrates a solution in which prior to communications with theIPG 100, the external controller 254 will instruct the external charger252 to shut off, and then to turn back on if necessary, i.e., if thecharger was operating in the first place. Because the externalcontroller 254 automatically shuts off operations of external charger252, it is no longer necessary for the user to manually discontinuecharging before beginning communications between the external controller254 and the IPG 100. This makes operation by the user much simpler whileat the same time ensuring that there is no interference. In a preferredembodiment, the external controller 254 always sends at least onecommand to suspend the external charger 252 before communicating withthe IPG 100, even if it is unnecessary because the charger 252 is notcurrently engaged.

In FIG. 9D, the external controller 254 suspends operation of theexternal charger 252 during period 500; communicates with the IPG 100during period 501; and recommences charging (if necessary) in period502. In period 500, the external charger sends commands TC5 and TC6 tothe external charger to suspend charging, which occurs in the samemanner as commands TC1 and TC2 describes previously (FIG. 9B). Theexternal charger 252 can confirm that it has suspended charging in reply331. If the external charger 252 is not currently engaged in charging,it may additionally inform the external controller 254 of that fact inreply 331. If the external charger 252 is not present at all, e.g., ifit is distant from the patient and out of communication reach, then noacknowledgment AK 327 is received at the external controller 254, whichcan then simply begin communications with the IPG 100 during period 501.

While period 500 in FIG. 9D only shows the external controller 254shutting down the charging field 401, it is understood that similarinstructions TC5 and TC6 can be used to shut down any operation that theexternal charger 252 is carrying out with the IPG 100. For example, ifthe external charger 252 were in the process of requesting charginginformation from the IPG 100 (as shown by command TI1 in FIG. 9C), theexternal controller 254 will automatically shut off any FSKcommunication between the external charger 252 and the IPG 100 duringthe time that the external controller 254 wants to communicate with theIPG 100.

In period 501, the external controller 254 communicates with the IPG100, using commands TI2 and TI3, and the type of handshaking procedurealready discussed. Alternatively, communications between the externalcontroller 254 and IPG 100 can take place in any manner as they occur inlegacy systems. Typically, commands sent from the external controller tothe IPG 100 represent some information that the external controller 254wants to send to the IPG 100. Such information can relate to statusinquiries, wake up messages, power down messages, turning stimulationon/off, level or amplitude of stimulation pulses, duration or frequencyof stimulation pulses, selection of electrodes to be activated, etc. Theexternal controller 254 will compile this information into appropriatecommands (such as TI2 and TI3) that can be understood by the IPG 100. Ofcourse, the exact format of the commands will correspond to the type ofIPG 100. Communication between the external controller 254 and the IPG100 can also include information transmitted from the IPG 100 to theexternal controller 254. Two examples of such communication are shown byway of messages AK and RP in period 501.

Once these communications are complete, the external controller 254 canonce again instruct the external charger 252 to commence charging duringperiod 502. Once again, this can occur using commands TC7 and TC8 andthe handshaking procedure already discussed. However, it is not strictlynecessary to issue commands TC7 and TC8 to recommence charging. Forexample, if the external charger 252 was not producing a charging field,which would be evident based on a lack of an acknowledgment 327 or anindication of no charging in the reply 331, the external controller 254may dispense with sending commands to recommence charging during period502. In fact, this may be preferred to prevent unwanted engagement ofthe external charger 252. Alternatively, it may be harmless to send thecommands TC7 and TC8 to recommence charging in any event: if theexternal charger 252 is out of range, such commands will once againsimply not be acknowledged (352); if the external charger 252 was notpreviously engaged in charging—for example, if the charger had not beenturned on by the user—it can choose to simply ignore the commands. Ifthe external charger 252 was engaged in charging, it can confirmrecommencement of charging to the external controller 254 in reply 356,and can continue providing charging information to the externalcontroller 254 in the manners previously described.

Although not shown in FIG. 9D for simplicity, it should be understoodthat commands TC7 and TC8 may instruct the external charger 252 to enterthe default fast data transmit mode. This might be beneficial to wardagain the possibility that the external charger 252 became misalignedwhile it was suspended during period 501, a problem better handledduring the fast mode as described earlier.

Although discussed in the context of providing charging information tothe external controller 254, it should be recognized that thecommunicative flexibility provided by modifications to the externalcharger 252, and the FSK links 251 and 266 it supports, can be put toother beneficial uses in the system 201. This disclosure shouldtherefore not be limited in its applicability to that context.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

What is claimed is:
 1. A method for operating an implantable medicaldevice system, comprising: charging an implantable medical device with acharging field generated from a coil in an external charger; andcommunicating, using the coil in the external charger, with an externalcontroller, wherein a proportion of time that the coil in the externalcharger is used for the act of communicating is determined based on adegree of alignment between the external charger and the implantablemedical device.
 2. The method of claim 1, wherein the proportion of timeduring which the coil in the external charger is used for the act ofcommunicating is greater when the degree of alignment between theexternal charger and the implantable medical device is lower.
 3. Themethod of claim 1, wherein the act of communicating comprises sendingcharging information to the external controller.
 4. The method of claim3, further comprising conveying the charging information to a user via auser interface of the external controller.
 5. The method of claim 4,wherein the user interface is a graphical user interface.
 6. The methodof claim 1, wherein the act of communicating comprises operating in oneof two data transmit modes, comprising: a fast data transmit mode inwhich a first proportion of time is used for the act of communicating;and a slow data transmit mode in which a second proportion of time isused for the act of communicating, wherein the second proportion issmaller than the first proportion.
 7. The method of claim 6, wherein theact of communicating comprises initializing communications between theexternal charger and the external controller.
 8. The method of claim 7,wherein the act of communicating comprises defaulting to the fast datatransmit mode after the communications are initialized.
 9. The method ofclaim 8, wherein the act of communicating comprises transitioning to theslow data transmit mode when a determined degree of alignment isobserved.
 10. The method of claim 6, wherein the act of communicatingcomprises sending information regarding the alignment between theexternal charger and the implantable medical device in the fast datatransmit mode.
 11. The method of claim 1, wherein the act ofcommunicating comprises periodically interrupting the act of charging tolisten for communications from the external controller.
 12. Animplantable medical device system, comprising: an implantable medicaldevice; an external controller for communicating with the implantablemedical device; and an external charger comprising a coil, the externalcharger configured to: generate a charging field, using the coil, forproviding energy to the implantable medical device; and periodicallysuspend generation of the charging field to communicate with theexternal controller using the coil, wherein a proportion of time duringwhich generation of the charging field is suspended is determined basedon a degree of alignment between the external charger and theimplantable medical device.
 13. The system of claim 12, wherein theproportion of time during which generation of the charging field issuspended is greater when the degree of alignment between the externalcharger and the implantable medical device is lower.
 14. The system ofclaim 12, wherein the external charger is configured to communicatecharging information to the external controller during the suspension ofthe generation of the charging field.
 15. The system of claim 14,wherein the charging information comprises information regarding thedegree of alignment between the external charger and the implantablemedical device.
 16. The system of claim 12, wherein the external chargercomprises a tuning circuit coupled to the coil, wherein the tuningcircuit is configured to tune the coil to a first frequency forgenerating the charging field and a second frequency for communicatingwith the external controller.
 17. The system of claim 12, wherein theexternal charger is configured to generate the charging field and toperiodically suspend generating the charging field in accordance withone of two operational modes, comprising: a fast data transmit mode inwhich the generation of the charging field is suspended for a firstproportion of time; and a slow data transmit mode in which thegeneration of the charging field is suspended for a second proportion oftime, wherein the second proportion is smaller than the firstproportion.
 18. The system of claim 17, wherein the external charger isconfigured to communicate information regarding the degree of alignmentbetween the external charger and the implantable medical device usingthe fast data transmit mode.
 19. The system of claim 17, wherein theexternal charger is configured to communicate charging information tothe external controller using the slow data transmit mode.
 20. Thesystem of claim 19, wherein the external controller comprises a userinterface for conveying the charging information to a user.